[openstack-dev] [Heat] rough draft of Heat autoscaling API

Fox, Kevin M kevin.fox at pnnl.gov
Thu Nov 21 18:31:01 UTC 2013

There is a high priority approved blueprint for a Neutron PoolMember:

From: Christopher Armstrong [chris.armstrong at rackspace.com]
Sent: Thursday, November 21, 2013 9:44 AM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [Heat] rough draft of Heat autoscaling API

On Thu, Nov 21, 2013 at 5:18 AM, Zane Bitter <zbitter at redhat.com<mailto:zbitter at redhat.com>> wrote:
On 20/11/13 23:49, Christopher Armstrong wrote:
On Wed, Nov 20, 2013 at 2:07 PM, Zane Bitter <zbitter at redhat.com<mailto:zbitter at redhat.com>
<mailto:zbitter at redhat.com<mailto:zbitter at redhat.com>>> wrote:

    On 20/11/13 16:07, Christopher Armstrong wrote:

        On Tue, Nov 19, 2013 at 4:27 PM, Zane Bitter <zbitter at redhat.com<mailto:zbitter at redhat.com>
        <mailto:zbitter at redhat.com<mailto:zbitter at redhat.com>>
        <mailto:zbitter at redhat.com<mailto:zbitter at redhat.com> <mailto:zbitter at redhat.com<mailto:zbitter at redhat.com>>>> wrote:

             On 19/11/13 19:14, Christopher Armstrong wrote:

        thought we had a workable solution with the "LoadBalancerMember"
        which you would use in a way somewhat similar to
        in the above example, to hook servers up to load balancers.

    I haven't seen this proposal at all. Do you have a link? How does it
    handle the problem of wanting to notify an arbitrary service (i.e.
    not necessarily a load balancer)?

It's been described in the autoscaling wiki page for a while, and I
thought the LBMember idea was discussed at the summit, but I wasn't
there to verify that :)


Basically, the LoadBalancerMember resource (which is very similar to the
CinderVolumeAttachment) would be responsible for removing and adding IPs
from/to the load balancer (which is actually a direct mapping to the way
the various LB APIs work). Since this resource lives with the server
resource inside the scaling unit, we don't really need to get anything
_out_ of that stack, only pass _in_ the load balancer ID.

I see a couple of problems with this approach:

1) It makes the default case hard. There's no way to just specify a server and hook it up to a load balancer like you can at the moment. Instead, you _have_ to create a template (or template snippet - not really any better) to add this extra resource in, even for what should be the most basic, default case (scale servers behind a load balancer).

We can provide a standard resource/template for this, LoadBalancedServer, to make the common case trivial and only require the user to pass parameters, not a whole template.

2) It relies on a plugin being present for any type of thing you might want to notify.

I don't understand this point. What do you mean by a plugin? I was assuming OS::Neutron::PoolMember (not LoadBalancerMember -- I went and looked up the actual name) would become a standard Heat resource, not a third-party thing (though third parties could provide their own through the usual heat extension mechanisms).

(fwiw the rackspace load balancer API works identically, so it seems a pretty standard design).

At summit and - to the best of my recollection - before, we talked about scaling a generic group of resources and passing notifications to a generic controller, with the types of both defined by the user. I was expecting you to propose something based on webhooks, which is why I was surprised not to see anything about it in the API. (I'm not prejudging that that is the way to go... I'm actually wondering if Marconi has a role to play here.)

I think the main benefit of PoolMember is:

1) it matches with the Neutron LBaaS API perfectly, just like all the rest of our resources, which represent individual REST objects.

2) it's already understandable. I don't understand the idea behind notifications or how they would work to solve our problems. You can keep saying that the notifications idea will solve our problems, but I can't figure out how it would solve our problem unless someone actually explains it :)

IRC: radix
Christopher Armstrong

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